1898.] NATURAL SCIENCES OF PHILADELPHIA. 115 



support, drops of water containing many frustules were suspended on 

 cover-glasses and observed. The diatoms were found to separate into 

 two portions. The first remained attached to the glass ; such of 

 them as had their dorsal or convex girdles next the glass performed 

 the revolution before described ; and these, with the others in con- 

 tact with the cover, proceeded in characteristic ways, with the curi- 

 ous and significant difference, that as viewed from above the ventral 

 side was now uppermost. The second portion fell to the surface of 

 the suspended drop, where they moved as if upon a solid substratum. 

 Midway of the drop there were none. Undoubtedly the surface of 

 the drop possessed sufficient tension for the purposes of a crawling 

 diatom. I have seen, in an aquarium, small snails crawling freely 

 along the plane of contact between water and air, with broad, flat 

 foot uppermost, applied to the surface of the liquid as if to a piece 

 of glass. 



Phenomena in carbon emulsion. — All preceding observations seem- 

 ing to point to the existence of invisible organs functioning as pseu- 

 dopodia, the endeavor was made to outline these by the well-known 

 method of putting the diatoms in an emulsion of colored particles 

 finely divided. To this end, since available India ink was found to 

 be toxic owing to its content of camphor, a portion of carbon-black 

 water-color was rubbed up in a drop of water until a very dark color 

 was obtained. The emulsion showed, under medium powers, a mul- 

 titude of particles exhibiting the Brownian movement. When placed 

 in this, the errant Eunotia cells revealed quite clearly the existence 

 at the corners of rounded masses of coleoderm. These were espe- 

 cially clear at the anterior corners. The particles of carbon ap- 

 proached the frustules quite closely everywhere except about the 

 corners, and a little U-shaped line, composed of somewhat compacted 

 particles, preceded the moving diatom. There was nowhere observa- 

 ble any streaming away of the particles, such as that seen by H. 

 L. Smith and others in Pinnularia. Owing to the tenacity of the 

 emulsion, and partly perhaps to the relatively raised position of the 

 posterior end of the frustule, the clear spaces are less evident at the 

 posterior corners. 



Results of staining. — Numerous attempts were made with a va- 

 riety of stains to render the coleoderm visible, the presence of which 

 seemed to be so strongly indicated. All efforts to stain the still 

 living coleoderm failed entirely. There was little better success in 

 fixing with osmic acid and staining with methylene blue, methyl 



